The present invention relates generally to an ultrasonic transducer and more particularly to an ultrasonic transducer having a non-bonded piezoelectric film to increase high frequency response and ease of repair.
A common technique for the nondestructive testing of small intricate parts for flaws in their materials, welds, brazes, solid-state bonds, etc. involves the use of high-resolution immersion transducers. For these applications, the device under test is immersed in a tank of water and a transducer is passed over the surface of the device. Ultrasonic pulses from the transducer reflect off the outer and inner surfaces of the device under test and are received by the transducer and analyzed. If a flaw occurs on the hidden side of the device under test, the output from the transducer to a receiver amplifier changes, providing an indication of the flaw.
Existing ultrasonic transducers are constructed from a plurality of layers of different materials bonded together. For example, U.S. Pat. No. 4,296,349 of T. Nakanishi et al. shows a conventional transducer to comprise a piezoelectric film 4 sandwiched by a pair of thin electrodes, with one electrode being bonded to a substrate. An embodiment of this invention shows an additional protector layer of nylon or similar material bonded to the other electrode. The electrode is a metal such as copper or gold which is formed on one surface of the piezoelectric film by means of evaporation, sputtering, or plating. The patent also states that the electrode can be formed by thin metal foil, although no example of such film is given and no structure for forming such a transducer is shown.
U.S. Pat. No. 4,297,607 of L. Lynnworth references a microprobe developed by Wilson et al. and reported in the IEEE 1979 Ultrasonics Symposium Proceedings as having a PVF2 transducer of 30 um. thick coupled directly to a front sealant stainless steel shim (of 25 um.) by a combination of pressure and oil. These construction details are not substantiated by the proceedings, which does indicate that the transducer diameter is 1.5 mm. and that the maximum frequency response of the device was 10 MHz. The small size of the device enables its use in medical applications.